Vehicle Regulating System and Method for Determining Tire States

ABSTRACT

A control device for a vehicle regulating system is configured to pick up driving state measurement signals from driving state sensors of the vehicle and determine reaction properties of the vehicle wheels from the signals. The control device is configured to also pick up roadway measurement signals of a spectroscopic sensor that is aligned with a roadway surface and determine therefrom the presence and/or properties of a layer of water on the roadway surface. The control device determines tire properties of the tires on the basis of the determined reaction properties of the vehicle wheels and the roadway measurement signals.

FIELD OF THE INVENTION

The invention generally relates to a control device for a vehicleregulating system, and to a method for determining tire states ofvehicle tires.

BACKGROUND OF THE INVENTION

Vehicle tires serve to transmit all the forces and torques between thevehicle and the roadway. For this reason, monitoring or checking of thetires permits vehicle regulating systems to be set better and, ifappropriate, hazardous situations to be detected.

For this purpose it is known, on the one hand, to measure and to monitorthe air pressure in vehicle tires. Furthermore, wear sensors are knownthat, if appropriate, can contribute to detecting a hazardous situationin the case of excessive wear of the tire profile.

DE 101 19 352 CI describes a method for determining the profileproperties of a vehicle tire, wherein microwaves are emitted byclose-range radar sensors assigned to the tires, and the profile depthof the vehicle tires can therefore be determined.

DE 100 58 099 A1 describes a method and a device for detecting orestimating abrasion of a tire, in which vehicle movement dynamicsvariables and other measurement variables that influence the abrasion ofthe tire are sensed during the normal operation of a vehicle by drivingstate sensors of the vehicle regulating systems using sensor signals,and the variables are stored and evaluated for approximate detection ofthe tire state or tire wear.

WO 2009/089972 A1 describes a method for distributing the driving torqueamong the wheels of a vehicle as a function of the tire state. In thiscontext, tires with low air pressure can be detected automatically bymeans of air pressure sensors or else on the basis of the wheel speeds.Furthermore, the wear or the profile depth of the individual wheels canbe determined by means of a sensor system.

EP 1 549 536 B1 describes improvements of the vehicle stability control,wherein tire force properties are included. In this context, thepressure of a tire is determined by means of a sensor, from which tireforces can be estimated and information about the reaction of thevehicle to a driver input can be estimated, in order to determine anactive correction for the wheel lock angle, the braking torque and/or adriving torque.

Furthermore, spectroscopic sensors are known with which surfaces can bedetected. Such spectroscopic sensors can also be used from a vehicle.

SUMMARY OF THE INVENTION

Generally speaking, it is an object of the present invention todetermine a tire state of a vehicle with relatively low outlay andrelatively high safety.

According to an embodiment of the present invention, the roadway surfacecan be examined spectroscopically. In this context, a spectroscopicsensor is used, in particular, to examine whether a water layer orwetting of the roadway surface with water is present, wherein for thispurpose, in particular, the level of the water layer and/or theaggregate state of the water can be determined.

By means of spectroscopic examination in relevant absorption bands ofwater (H₂O), the aggregate state of the water can also be detected. Inthis context, apart from IR radiation it is also possible to use lightin the visible range. It is therefore possible to take into accountwhether liquid water or else frozen water, i.e., snow or ice, ispresent, wherein these aggregate states bring about significantlydifferent grip properties of the vehicle tire. Furthermore, the level ofthe water layer can also be detected spectroscopically since, in thecase of spectroscopic examination, a sufficient penetration depth of theemitted IR radiation into a water layer is present, in order to detect arelatively large water depth as a relatively strong signal.

Light or IR radiation can be used for this in at least three differentwavelengths, for example 1460 nm for detecting water, 1550 nm fordetecting ice, and 1300 nm as a reference wavelength.

The optical sensor can be, in particular, a surface sensor. The use ofan optical surface sensor has the advantage that the actual roadwaycondition can be measured particularly reliably and without contact. Inaddition, in the case of a stationary vehicle, the optical surfacesensor also supplies information about the condition of the roadway. Theoptical surface sensor can comprise a light source unit for emittinglight of at least one wavelength onto the underlying surface, and atleast one detector for detecting light reflected by the underlyingsurface.

The surface sensor can comprise both a first detector and a seconddetector, wherein the first detector is suitable for sensing diffuselyreflected light, and the second detector for sensing light reflected ina mirroring fashion. It is possible to provide at least two polarizers,wherein a first polarizer with a first polarization device is assignedto the first detector. A light source polarizer can be assigned to thelight source unit, and/or a second polarizer can be assigned to thesecond detector. The polarization direction/directions of the secondpolarizer is/are oriented essentially perpendicular with respect to thefirst polarization direction of the first polarizer. If at least twopolarizers or polarization filters are provided, the first polarizer isarranged on the first detector, which only transmits light waves to thefirst detector in the first polarization direction. If a light sourcepolarizer is provided on the light source unit, the polarizationdirection of the light source polarizer is arranged essentiallyperpendicular with respect to the first polarization direction of thefirst polarizer, and the light emitted by the sensor is polarized in adirection essentially perpendicular with respect to the firstpolarization direction, with the result that light that is polarized atthe first detector and reflected in a mirroring fashion is filtered outand only diffusely reflected light is detected. A similar effect can beachieved if a second polarizer is arranged in front of the seconddetector and its polarization direction is oriented essentiallyperpendicular with respect to the first polarization direction. Thesecond polarizer can be used as an alternative to, or in addition to,the light source polarizer. It is also possible to provide for lightthat is already polarized to be generated in the light source unit. Thelight source unit can be configured to emit light of at least twodifferent wavelengths or to emit a plurality of wavelengths onto theunderlying surface or the roadway surface. For this purpose, the lightsource unit can comprise, for example, a plurality of light sources. Theuse of at least two wavelengths, preferably three different wavelengths,permits the sensor to be operated in a spectral fashion. By usingwavelengths that are, for example, particularly well absorbed by ice orwater, ice or water on the roadway or roadway surface can be detected ifthe reflected light with the wavelength absorbed by the water or ice iscompared with that of a reference wavelength. It is therefore possibleto implement the principles of the spectral analysis and of diffusereflection and mirroring reflection in only one device or a singlehousing. The light source unit, the first detector and, if appropriate,the second detector can for this purpose be arranged, for example,directly next to one another in a common single and/or single-piecehousing.

It is possible to use light in at least three different wavelengths inthe infrared range. The light source unit can, for this purpose,comprise a plurality of light sources. For example, the light sourceunit can be configured to emit infrared light with the wavelengths 1300nm, 1460 nm and 1550 nm, while light with the wavelength 1460 nm isparticularly well absorbed by water, and light with the wavelength 1550nm is well absorbed by ice. Light in the region of approximately 1300 nmcan then be used as a reference wavelength. However, other wavelengthscan also be used. In particular, for the reference wavelength it ispossible to use any other wavelength that is appreciably absorbedneither by ice nor by water. Any other wavelength that is absorbed to anincreased degree in water can also be used as a water-sensitivewavelength. Likewise, any wavelength that is absorbed to an increaseddegree in ice can be selected as an ice-sensitive wavelength. Otherwavelengths of interest comprise, for example, 1190, 1040, 970, 880 and810 nm in the infrared range as well as the visible wavelengths 625, 530and 470 nm.

The light source unit can be configured to emit light with preciselythree different wavelengths. For this purpose, the light source unit canhave three light sources, one light source for each wavelength. Only thethree wavelengths are used in order to sense both light that isreflected spectrally and light that is reflected in a mirroring/diffusefashion, in order to determine and/or detect both the condition of theroadway and the type of the roadway. Any of the light sources can beactuatable individually and can be capable of being switched on and offindependently of the others and/or can be regulated in terms of theirintensity.

Furthermore, more than the abovementioned two or three differentwavelengths can also be used. For example, the wavelength 625 nm canalso be used to measure the light reflected in a diffuse and mirroringfashion.

It is also possible to provide for the emitted light to be modulated inintensity and/or amplitude. The modulation of the intensity or amplitudecan take place by switching all of the light sources or individual lightsources of the light source unit on and off. The modulation of theintensity or the switching on and off can take place separately for eachwavelength of the light source unit or for each light source of thelight source unit. For example, the modulation of the amplitude orintensity or the switching on and off can take place at the samefrequency but with a phase shift and/or at different frequencies foreach wavelength. As a result, it is possible to ensure, for example,that the light with different wavelengths is emitted in achronologically staggered fashion or sequentially. For example, it ispossible to provide for light with a first wavelength to be emitted fora specific time interval and then the light with the first wavelength tobe switched off and a second wavelength to be switched on etc. In eachcase light of just one wavelength is then detected in the detectors. Asa result, a spectral analysis or splitting of the incident light at thedetectors can be avoided. Mixed forms of different modulation techniquescan also be applied, in particular frequency-modulated andamplitude-modulated optical signal lines with or without interruptions.

It is therefore also possible to use simple detectors as the first orsecond detector. For example, photodiodes can be used. The firstdetector and the second detector can each comprise one or morephotodiodes. At least the first detector can be configured to senselight with all the wavelengths emitted by the light source unit. Thedetector can also alternatively or additionally comprise anoptoelectronic chip (for example CCD) or some other optical recordingdevice.

The first and the second detector can be used to sense and/or determinelight that is reflected in a mirroring fashion and light that isreflected in a diffuse fashion. In addition, at least one of the firstand second detectors can also be used for the spectral determination. Atleast this detector is then configured to detect light with a pluralityof wavelengths. In this example, the sensor has precisely the firstdetector and the second detector and no further detectors are provided.

The surface sensor can also comprise an evaluation device that outputsinformation about the condition of the roadway surface or the underlyingsurface.

The surface sensor is also suitable for detecting the thickness of awater film on the roadway surface or the thickness of an ice layer, withthe result that, for example in the case of a wet roadway, theinformation is not transmitted to the vehicle driver until there is aspecific water film thickness at which, for example, aquaplaning canarise.

According to the inventive embodiments, it is therefore possible toevaluate a reaction of the tires to respectively acting longitudinalforces and/or lateral forces or corresponding torques. For this purpose,the forces and torques acting at the tires are determined from thevehicle movement dynamics measurement variables and/or driving statemeasurement variables of the vehicle sensors, and also the reaction ofthe vehicle or its wheels to these acting forces and torques. The slipbehavior of the individual tires can therefore be determined, inparticular as frictional values and/or as grip in the wet, but also inthe longitudinal direction and/or lateral direction, wherein this slipbehavior can be determined, in particular, as a function of the state ofthe water and then relate to the acting forces and/or torques. Forexample, the loss of grip in the wet, risk of aquaplaning or lack ofall-year properties (off-road and snow) can be determined.

As a result, actual values that are determined for the slip behavior orcoefficient of friction behavior can be compared with the determinedproperties of the roadway surface, i.e., in particular a possiblypresent water layer and the level and aggregate state thereof.

This comparison permits, on the one hand, conclusions to be made aboutthe tire state; it is possible to determine whether the tire state, inparticular the profile depth, permits the behavior or the coefficient offriction that is to be expected with the given surface state or wettingof the roadway surface with water. The tire state can therefore beevaluated for the given water conditions. For this purpose, setpointvalues or stored reference values relating to the behavior of a tire onroadways can advantageously be compared as a function of correspondingwater properties, i.e., corresponding level and relevant aggregate stateof the water layer present.

Since, therefore, the tire state is known, it is possible, on the onehand, to output a warning signal when a very poor tire state isdetected, i.e., a high degree of abrasion of the profile depth and/orhardening of the tread rubber mixture. Furthermore, the assessment ofthe tire state can also be taken into account in the vehicle regulatingsystem, for example a vehicle stability system or ABS. As a result, theprevailing frictional engagement potential of the tires can be utilizedbetter; the regulating process can permit forces and/or torques, whichoccur in principle, to such an extent that they utilize this frictionalengagement potential or the individual coefficients of friction on therespective roadway states.

The coefficient of friction behavior or behavior of the tire on theroadway is therefore determined directly without having to have recourseto theoretical data such as the age of the tire or data about the rubbermixture of the tires for this purpose. This permits advantages sincedata about the aging of the tire do not always also take into accountthe actual loads and the actual wear and the aging owing to unfavorableweather states such as temperature effects or solar radiation effects onthe tires.

The properties of the vehicle tire, in particular also relating to theloss of grip in the wet, risk of aquaplaning or lack of off-road andsnow properties, can furthermore also be indicated and/or logged.

Still other objects and advantages of the present invention will in partbe obvious and will in part be apparent from the specification.

The present invention accordingly comprises the several steps and therelation of one or more of such steps with respect to each of theothers, and embodies features of construction, combination of elements,and arrangement of parts adapted to effect such steps, all asexemplified in the detailed disclosure hereinafter set forth, and thescope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below using an embodimentand with reference to the appended drawings, of which:

FIG. 1 shows a vehicle according to an embodiment of the invention on aroadway in a plan view;

FIG. 2 shows a side view of the vehicle depicted in FIG. 1; and

FIG. 3 is a flowchart of a method according to an embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vehicle 1 is traveling on a roadway 2, for example on a bend withsteering wheel lock and obliquely positioned front wheels 3. The vehicle1 has a vehicle movement dynamics regulating system and/or drivingstability regulating system having a control device 4, ABS sensors 5 onpreferably all the wheels, i.e., the front wheels 3 and rear wheels 6,as well as further vehicle movement dynamics sensors, for example a yawrate sensor 8 for measuring a yaw rate to as well as a lateralacceleration sensor 9 for measuring a lateral acceleration aq.

Furthermore, a spectroscopic sensor 10 is provided in the vehicle 1, andis directed at the roadway 2, for example in the front region of thevehicle 1. The spectroscopic sensor 10 preferably operates in the IR(infrared) wavelength range and detects absorption bands of water (H₂O)by emitting IR radiation IR and detecting IR radiation IR reflected bythe roadway surface 2 a of the roadway 2.

The ABS sensors 5 output wheel speed measurement signals S1 as firstmeasurement signals to the control device 4; correspondingly the yawrate sensor 8 outputs a yaw rate measurement signal S2 as the secondmeasurement signal, and the lateral acceleration sensor 9 outputs alateral acceleration measurement signal S3 as the third measurementsignal to the control device 4.

The spectroscopic sensor 10 outputs a roadway measurement signal S4 asthe fourth measurement signal to the control device 4. In contrast tothe measurement signals S1, S2, S3, measurement signal S4 does notsupply any driving state variable of the vehicle 1, but instead suppliesdata about the spectroscopic composition of the roadway surface 2 a ofthe roadway 2. The spectroscopic sensor 10 is advantageously configuredsuch that it detects the concentration of water on the roadway surface 2a, in particular also the level h of a water film 12, or as part of theroadway surface 2 a. Furthermore, the measurement signals S4 of thespectroscopic sensor 10 contain information about the aggregate state ofthe water film 12 or of water on the roadway surface 2 a. Thespectroscopic sensor 10 can therefore detect, for example, whether thewater or the water film 12 is or is not frozen.

The spectroscopic sensor 10 has a light source unit and one or moredetectors. The light source unit can use light in at least threedifferent wavelengths in the infrared range or else in the visiblerange. The light source unit can, for this purpose, comprise a pluralityof light sources. For example, the light source unit can be configuredto emit IR radiation with the wavelengths 1300 nm, 1460 nm and 1550 nm.While IR radiation with the wavelength 1460 nm is absorbed particularlywell by water, IR radiation with the wavelength 1550 nm is well absorbedby ice. IR radiation in the region of approximately 1300 nm can then beused as a reference wavelength. However, other wavelengths can also beused. In particular for the reference wavelength, it is possible to useany other wavelength that is appreciably absorbed neither by ice norwater. Any other wavelength that is absorbed to an increased degree inwater can also be used as a water-sensitive wavelength. Likewise, anywavelength that is absorbed to an increased degree in ice can beselected as an ice-sensitive wavelength. Other wavelengths of interestcomprise, for example, 1190, 1040, 970, 880 and 810 nm in the infraredrange as well as the visible wavelengths 625, 530 and 470 nm.

A velocity v of the vehicle 1 can be formed, for example, from the wheelspeed measurement signals SI and/or a rotational speed of an outputshaft of the vehicle transmission. A longitudinal acceleration a cancorrespondingly be determined therefrom.

For example, a slip angle a of the front wheels 3 is also determinedfrom the steering wheel lock or from a suitable sensor. Furthermore, themass, wheel base and track width of the vehicle may be known and storedin the control device 4 or an external memory.

After the start of the method in step 19, for example when the entirevehicle regulating system 7 starts, in step 20, 21 according to FIG. 3reaction properties of the vehicle wheels 3, 6 are firstly determined,wherein these reaction properties are here the longitudinal slip txand/or lateral slip ty. For this purpose, for example firstly in step 20it is determined, from the measured driving state values or from thedriving state values determined by means of the signals SI, S2, S3,whether appreciable longitudinal forces Fx or side forces Fy and/oracting torques Mω are present, for example whether a regulatingintervention of the regulating system is present as a result ofoutputting of a braking control signal S6 to a brake 14 or can bepresent soon under certain circumstances. In step 21, the slip behaviorof the wheels 3, 6 is then determined, for example at what forces Fx, Fyor torques Mω, like the yaw torque indicated in FIG. 1, the tires losegrip, for example by means of the longitudinal slip tx in the case of anABS intervention or traction control system intervention or by means ofthe slip angle a for the lateral slip ty.

In step 22, reaction properties of the tires 3 a, 6 a of the vehiclewheels 3, 6 are then determined, for example as coefficients offriction, from the acting forces Fx, Fy and/or torques Mω and the slipbehavior tx, ty.

In step 24, the roadway measurement signals S4 are picked up.

In step 26, the determined properties of the roadway surface 2 a arecompared with the determined reaction properties of the tires 3 a, 6 a,in order to acquire data about the grip in the wet, aquaplaningproperties and grip off-road and in snow. As a result, coefficients offriction can be acquired as a function of the water conditions.

In step 28, the tire state of the wheels 3, 6 is evaluated. As a resultit is possible to evaluate whether the reaction behavior is appropriateto the state of the roadway surface, for example whether a lowcoefficient of friction corresponds to a relevant water film 12 or not.If no water film 12 or no ice or snow is detected, better reactionproperties are to be expected, and otherwise it is possible to inferpoor tire properties.

In step 30, it is possible to output, if appropriate, tire state signalsS5, for example as warning signals, as a function of this determinationif an inadequate tire state is detected, for example in the case ofexcessively poor reaction properties of the tires 3 a, 6 a. The tirestate signals S5 can be output as display signals, for example to adisplay device in the vehicle 1 or for evaluation in the vehiclemovement dynamics regulating system.

If tire wear sensors are provided in the tires 3 a, 6 a, the measurementsignals of the sensors can be compared with the tire state propertiesdetermined. However, the determined tire state properties are morecomprehensive and can also, for example, take into account hardening ofthe tread rubber mixture, unequal abrasion, in particular of the profiledepth etc., of the tires 3 a, 6 a. If tire pressure sensors are alsoprovided for measuring the air pressure in the tires 3 a, 6 a, themeasurement signals thereof can be additionally used in order to takeinto account in step 26 the air pressure of the tires 3 a, 6 a, whichair pressure correspondingly influences their grip and therefore thereaction to instabilities or possible slip.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained, andsince certain changes may be made in the above processes andconstructions without departing from the spirit and scope of theinvention, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings shall be interpretedas illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention that, as amatter of language, might be said to fall therebetween.

What is claimed is:
 1. A control device for a vehicle regulating system, comprising: electronics configured to (i) receive driving state measurement signals transmitted from driving state sensors of the vehicle, (ii) determine reaction properties of wheels of the vehicle from the driving state measurement signals, (iii) receive roadway measurement signals of a spectroscopic sensor aligned with a roadway surface, (iv) determine from the roadway measurement signals at least one of the presence and properties of a water layer on the roadway surface, and (iv) determine tire properties of tires of the wheels based on the determined reaction properties of the wheels and the roadway measurement signals.
 2. The control device as claimed in claim 1, wherein the electronics are configured to determine a slip behavior of the vehicle wheels as reaction properties of the vehicle wheels based on the driving state measurement signals, at least one of forces and torques acting at the vehicle wheels, and at least one of forces and torques at which at least one of a longitudinal slip and a lateral slip of individual ones of the vehicle wheels starts.
 3. The control device as claimed in claim 2, wherein the electronics are configured to determine the slip behavior when the at least one of forces and torques are sufficiently large.
 4. The control device as claimed in claim 2, wherein the electronics are configured to determine the at least one of forces and torques acting at the vehicle wheels from at least one of longitudinal speed of the vehicle, longitudinal acceleration of the vehicle, lateral speed of the vehicle, lateral acceleration of the vehicle, yaw rate of the vehicle, and wheel speeds of the vehicle wheels.
 5. The control device as claimed in claim 1, wherein the electronics are configured to determine the presence and at least one of a level and aggregate state of the water layer on the roadway surface.
 6. The control device as claimed in claim 5, wherein the electronics are configured to use setpoint reaction properties of the tires from stored data and compare the setpoint reaction properties with determined actual reaction properties of the tires, and output an output signal as a function of the comparison.
 7. The control device as claimed in claim 6, further comprising a memory for storing initial new tire measurements as setpoint reaction properties of the tires.
 8. The control device as claimed in claim 5, wherein the reaction properties of the tires are friction values of the tires as a function of the aggregate state of at least one of the water layer and the level of the water layer.
 9. The control device as claimed in claim 1, wherein the spectroscopic sensor is configured for spectroscopic measurements at least partially in the infrared range.
 10. A vehicle regulating system, comprising: the control device as claimed in claim 1, driving state sensors configured to measure driving state measurement variables and output driving state measurement signals to the control device, and a spectroscopic sensor aligned with a roadway surface, the spectroscopic sensor configured to output roadway measurement signals to the control device, wherein the spectroscopic sensor is configured to determine at least one of an absorption behavior and reflection behavior of the roadway surface in a wavelength range suitable for water.
 11. A method for determining at least one tire state of a vehicle tire, comprising: using driving state sensors of the vehicle to receive driving state measurement signals, determining reaction properties of wheels of the vehicle based on the driving state measurement signals, receiving roadway measurement signals of a spectroscopic sensor that is aligned with a roadway surface, and determining at least one of a presence and properties of a water layer on the roadway surface based on the roadway measurement signals, and determining tire properties of the tires based on the determined reaction properties of the vehicle wheels and the roadway measurement signals.
 12. The control device as claimed in claim 2, wherein the electronics are configured to determine the slip behavior when a regulating intervention of the vehicle regulating system commences.
 13. The control device as claimed in claim 9, wherein the spectroscopic sensor is configured for spectroscopic measurements in three wavelength ranges comprising an absorption wavelength for detecting water of about 1460 μm, an absorption wavelength for detecting ice of about 1550 nm and a reference wavelength without relevant absorption of water or ice. 